We will determine the kinetics of equilibration of radioiodinated serum albumin between plasma and RTD lymph in control animals and in animals subjected to hemorrhagic shock and reinfusion. From the initial equilibration coefficient and from lymph to plasma ratios of chemically determined albumin, we should be able to calculate the change in the reflection coefficient and in the permeability-area product of capillaries drained by the RTD following hemorrhagic shock. We also wish to determine whether or not we can reproduce the changes in the pulmonary vascular shunt fraction (Qs/Qt) following hemorrhagic shock, by increasing the levels of circulating epinephrine and norepinephrine in non-shocked animals. In normal dogs, left lower lobe atelectasis produced by intrabronchial balloon inflation causes a mean increase in Qs/Qt from 8% to 19%. This increase is reduced by 80% over the ensuing 2 hours. We have previously reported that hemorrhagic shock abolishes the ability of the lung to reduce the shunt fraction following atelectasis. We will also compare RISA equilibration rates in RTD lymph to those calculated from lung biopsy specimens utilizing sulfate space as a measure of extracellular water, hemoglobin as an indicator for intravascular volume, and the difference between wet and dry weights to determine total lung water.